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JV

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Question about NoiseType = Jitter
Oct 22^nd, 2017, 1:19am

Hi all,

I have some confusions about my simulation setup for the noise of a VCO + buffer circuit, which is used inside a PLL.

The buffer converts the sinusoidal signal from the VCO to rail-to-rail square-wave signals which are driving subsequent frequency dividers.
Since the frequency dividers are edge-triggered, I'm using PSS+PNOISE analysis with NoiseType=jitter.

I am using Cadence version IC 6.1.7

- When I tick the NoiseType = jitter box, the PNOISE form talks about "PM jitter for autonomous circuits", shouldn't this be FM jitter since it's an autonomous circuit?

- When the simulation finishes and I go to the "Direct Plot" form, I can choose between Jee, Jc and Jcc jitter. However, I thought that Jee was defined for driven circuits only? What does Jee represent in this case?

Could someone explain please? Many thanks!

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Andrew Beckett

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me about Life...

Posts: 1742
Bracknell, UK

Re: Question about NoiseType = Jitter
Reply #1 - Dec 21^st, 2017, 6:18am

It's the edge to edge jitter of a single cycle. I'm not sure it's terribly useful though for an autonomous circuit...

Note that if using IC617 together with MMSIM151 or later, you get the "FM" jitter by picking noisetype=timeaverage, with one of the Contribution Types that includes PM (i.e. PM, AM&PM or all). This approach computes the jitter by computing the PM noise and then converting it to a jitter metric, whereas the "PM jitter" approach strobes the noise at a threshold crossing and combines that with the slope of the signal at the threshold crossing to compute the jitter.

In older versions using noisetype="jitter" gave you a choice of FM or PM jitter; if you picked FM, it actually ran the "modulated" mode - this has now been replaced by the new choices with noisetype=timeaverage and hence the FM choice has gone from noisetype=jitter. Using noisetype=jitter only ever computes PM jitter using the method described above.

Regards,

Andrew.

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JV New Member Offline Posts: 5 Belgium	Re: Question about NoiseType = Jitter Reply #2 - Dec 23^rd, 2017, 3:28am Thank you Andrew, for your reply, it made things more clear. Enjoy the christmas period!
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